JP2000184702A - Power supply equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply equipment of high efficiency by reducing a loss generated when a switching element is driven. SOLUTION: A connection between the emitters of transistors Q2, Q3 for driving a driving circuit 4 is connected to the base of a switching transistor Q1, and a connection between the bases of the transistors Q2, Q3 is connected to a pulse output terminal PO of a control circuit 3. The collector of the transistor Q3 is connected to a main current path of a control transistor Q4 which constitutes a limiter circuit 5. Furthermore, a current detecting circuit 6a for detecting the output current of the power supply equipment is installed, and a signal corresponding to the output current detected by the current detecting circuit 6a is supplied to the base of the control transistor Q4 of the limiter circuit 5. Between the base of the switching transistor Q1 and the pulse output terminal PO of the control circuit 3, a resistor 7 which constitutes a bias circuit 7 is connected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for reducing a loss generated when driving a current control element.

[0002]

2. Description of the Related Art Among various power supply devices, a switching type power supply device stabilizes an output voltage to a desired value by controlling an on / off operation of a switching element as a current control element. As an example of a circuit used in a switching power supply, there is a circuit having a configuration shown in FIG. The circuit shown in FIG. 4 has the following configuration.
In FIG. 4, reference numerals 1 and 2 denote input terminals and output terminals on the high potential side, and input terminals and output terminals on the low potential side are not shown, but are connected to a reference potential point, that is, the ground. Shall be. The switching transistor Q1 and the choke coil L1 are connected in series between the input terminal 1 and the output terminal 2, an output capacitor C2 is connected between one end of the output terminal side 2 of the choke coil L1 and the ground, and the choke coil L1 is connected. Diode D1 between the other end and ground
Is connected. A capacitor C1 is connected between the input terminal 1 and the ground.

[0003] Two driving transistors Q2 and Q3 having different polarities are connected between an input terminal 1 and the ground in such a manner that their emitters and bases are commonly connected.
The common connection point of the bases of the driving transistors Q2 and Q3 is connected to the input terminal 1 via a resistor R5, and a driving circuit 4 is formed by the driving transistors Q2 and Q3 and the resistor R5. The common connection point of the emitters of the driving transistors Q2 and Q3 is connected to the base of the switching transistor Q1 via a parallel circuit of a resistor R14 and a capacitor C3, and the common connection point of the bases of the driving transistors Q2 and Q3 is Is connected to the pulse output terminal PO. A resistor R1 and a resistor R are connected between the output terminal 2 and the ground.
2 are connected in series, and the connection point between the resistors R1 and R2 is connected to the voltage detection terminal FB of the control circuit 3.

The circuit of FIG. 4 having the above-described configuration has a circuit configuration generally called a step-down chopper type converter. The operation of the step-down chopper type converter is described in various documents, and the operation is briefly described as follows. First, the control circuit 3 generates a drive signal corresponding to the output voltage at the pulse output terminal PO. Then, the drive circuit 4 turns on and off the base current of the switching transistor Q1 according to the drive signal, and causes the switching transistor Q1 to perform a switching operation. With this switching operation, the switching transistor Q1
Flows into the capacitor C2 via the choke coil L1, and charges the capacitor C2. The voltage generated at both ends of the capacitor C2 is supplied from the output terminal 2 to an external load as a DC output voltage. This is the operation process.

[0005]

In the circuit shown in FIG. 4, when the load connected to the output terminal 2 is in the maximum operating state, the peak value of the current flowing through the main current path of the switching transistor Q1 has the maximum value. Become. In order to keep the switching transistor Q1 in the ON state with respect to a current having a large peak value passing through the main current path, it is necessary to supply a base current having a magnitude corresponding to the peak value of the current. Therefore, the resistance value of the resistor R14 is determined from the maximum value of the base current required at the time of the maximum load. On the other hand, when the load is in a state close to no load, for example, in a standby state, the peak value of the current flowing through the main current path of the switching transistor Q1 becomes a small value. In this case, theoretically, the base current for keeping the switching transistor Q1 in the ON state may be small.

However, it is the resistor R14 that determines the magnitude of the base current in the circuit having the configuration shown in FIG. 4, and the resistance value is determined by the base current required at the maximum load. Therefore, the circuit shown in FIG. 4 is in a state where the base current of the switching transistor Q1 flows more than necessary at a light load. Unnecessary extra base current flow causes extra power loss in the switching transistor Q1, the resistor R14, and the driving transistor Q3, causing a reduction in the overall efficiency of the power supply device. Therefore, an object of the present invention is to provide a power supply device that reduces the loss that occurs when a switching element as a current control element is driven and has high overall efficiency.

[0007]

According to the present invention, there is provided a switching power supply for obtaining a desired output voltage by changing a flow rate of a current passing through a current control element in accordance with a signal from a control circuit. A control circuit that outputs a pulse signal having a large on-duty, a control terminal having a drive transistor connected to the control circuit, and one end of a main current path connected to a control terminal of the current control element,
A drive circuit that supplies a bias to the current control element in response to a pulse signal from the control circuit, a current detection circuit that outputs a detection signal corresponding to the magnitude of an output current of the power supply device, and a drive circuit that is connected to the drive circuit. And a limiter circuit for changing the amount of bias supplied to the current control element via the current control circuit in accordance with a detection signal from the current detection circuit.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A drive circuit is formed by connecting control terminals of two drive transistors having different polarities to one end of a main current path. A common connection point between the control terminals of the drive circuit is connected to a pulse output terminal of the control circuit,
A common connection point between one ends of the main current path is connected to a control terminal of the switching element. A limiter circuit having a control transistor is provided, and a main current path of the control transistor is connected to a main current path of a driving transistor of the driving circuit. A current detection circuit for detecting an output current of the power supply device is provided, and a signal corresponding to the obtained output current is supplied to a control terminal of a control transistor of the limiter circuit.

A bias circuit is connected between a control terminal of the switching element and a pulse output terminal of the control circuit in order to make the switching element conductive when the power supply device is started. Alternatively, instead of the bias circuit, a current bypass circuit is connected in parallel with the main current path of the control transistor of the limiter circuit. With such a circuit configuration, the amount of bias supplied to the current control element via the drive circuit is changed according to the output current detected by the current detection circuit by the limiter circuit.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a circuit of a switching power supply according to the present invention, in which a loss generated when driving a switching element is reduced. The circuit shown in FIG. 1 has the following circuit configuration. In FIG. 1, the same components as those shown in the circuit of FIG. 4 are denoted by the same reference numerals.
The switching transistor Q1, the choke coil L1, and the primary winding N1 of the current transformer CT are connected in series between the input terminal 1 and the output terminal 2. The output capacitor C2 is connected between the connection point of the choke coil L1 and the primary winding N1 and the ground, and the diode D1 is connected between the connection point of the choke coil L1 and the switching transistor Q1 and the ground. A capacitor C1 is connected between the input terminal 1 and the ground.

Two driving transistors Q having different polarities
The emitters and bases of the transistors 2 and Q3 are commonly connected, and the collector of the driving transistor Q2 is connected to the input terminal 1. A common connection point of the bases of the driving transistors Q2 and Q3 is connected to the input terminal 1 via a resistor R5,
The driving circuit 4 is formed by the driving transistors Q2 and Q3 and the resistor R5. Driving transistors Q2, Q3
Is connected to the base of the switching transistor Q1 via a parallel circuit of a resistor R3 and a capacitor C3, and the common connection point of the bases of the driving transistors Q2 and Q3 is connected to the pulse output terminal PO of the control circuit 3. I do. The collector of the driving transistor Q3 is connected to the collector of the control transistor Q4, and the emitter of the control transistor Q4 is connected to the ground. The resistor R7 is connected between the base of the control transistor Q4 and the ground, and the base of the control transistor Q4 is connected to one end of the resistor R6. A limiter circuit 5 is formed by the control transistor Q4 and the resistors R7 and R6.

The other end of the resistor R6 is connected to one end of a capacitor C4, and the other end of the capacitor C4 is connected to ground. One end of the capacitor C4 is connected to one end of the secondary winding N2 of the current transformer CT via the diode D2, and the other end of the secondary winding N2 is connected to the ground. This capacitor C4,
A current detection circuit 6a is formed by the diode D2 and the current transformer CT. A resistor R1 and a resistor R2 are connected in series between the output terminal 2 and the ground.
2 is connected to the voltage detection terminal FB of the control circuit 3. A resistor R4 is connected between the base of the switching transistor Q1 and the pulse output terminal PO of the control circuit 3, and a bias circuit 7 is formed by the resistor R7.

In such a circuit configuration, when a voltage is supplied to the input terminal 1 from the outside, the control circuit 3 starts operating and causes a predetermined on-duty drive signal to appear at its pulse output terminal PO. . In the circuit of FIG. 1, when the voltage at the position of the pulse output terminal PO is low, the first path from the base of the switching transistor Q1 to the pulse output terminal PO via the resistor R4 and the resistor R3 from the base of the switching transistor Q1 The base current of the switching transistor Q1 flows in a second path from the parallel circuit of the capacitor C3, the driving transistor Q3 which has been turned on, and the ground via the control transistor Q4. Therefore, the switching transistor Q1 is biased by the base current flowing through each path according to the drive signal appearing at the pulse output terminal PO,
On / off operation is performed.

By the way, immediately after the start of the power supply, the voltage between the terminals of the capacitor C4 is almost zero, and the control transistor Q4 is in an off state. Therefore, the resistance R3 and the other second
No current can flow in the path of the resistor R4, and the switching transistor Q1 operates by receiving a bias only from the base current flowing through the first path of the resistor R4. Here, if an element having a high electric resistance is applied to the resistor R4, the resistance R4
, The base current of the switching transistor Q1 has a small value. As a result, the peak value of the current passing between the emitter and the collector of the switching transistor Q1 is limited to a small value, and the rush current flowing from the input terminal 1 is suppressed.

When the switching transistor Q1 is turned on by the base current passing through the resistor R4, the input terminal 1
Power transmission from the side to the output terminal 2 side is started. When a current flows through the primary winding N1 of the current transformer CT with power transmission, a voltage is induced on the secondary winding N2, and the capacitor C4 is charged via the diode D2. The voltage appearing between the terminals of the capacitor C4 is applied as a current detection signal corresponding to the output current to the base of the control transistor Q4 via the resistor R6. When the voltage between the terminals of the capacitor C4 increases, the control transistor Q4 becomes conductive, and the base current of the switching transistor Q1 also flows through the second path including the control transistor Q4.

A current passing through the control transistor Q4 as the voltage between the terminals of the capacitor C4 rises,
Current flowing through the path of the switching transistor Q1 also increases, and the total base current of the switching transistor Q1 gradually increases. Then, the peak value of the current passing between the emitter and the collector of the switching transistor Q1 gradually increases, and more current is supplied to the output capacitor C2 and the external load. After the output voltage and the output current are stabilized after a predetermined period, the circuit shown in FIG. 1 enters a steady operation state.

In a steady operation state, for example, when the load connected to the output terminal 2 reaches the maximum operating state, the output current of the circuit shown in FIG. 1 becomes very large. Then, the voltage between the terminals of the capacitor C4 charged by the voltage generated in the secondary winding N2 of the current transformer CT increases, and the control transistor Q4 is turned on. When the control transistor Q4 is turned on, the base current of the switching transistor Q1 has a maximum value substantially determined by the parallel resistance value of the resistors R3 and R4. On the other hand, when the load connected to the output terminal 2 reaches a minimum load state near no load, the output current of the circuit shown in FIG. 1 becomes very small. Then, the voltage between the terminals of the capacitor C4 becomes low, and the control transistor Q4 is turned off. Control transistor Q
When the transistor 4 is turned off, the base current of the switching transistor Q1 has the minimum value determined only by the resistor R4.

As a result, when the load is heavy, the base current of the switching transistor Q1 increases, and the output current required by the load is secured. On the other hand, when the load is light, the base current of the switching transistor Q1 is narrowed down, and the power loss generated in the circuit portion through which the base current flows is reduced. In other words, the circuit of FIG. 1 operates so that the required amount of base current of the switching transistor Q1 flows according to the output current required by the load, and thus the flow rate of the current that must pass through the main current path of the switching transistor Q1. I do. Additionally, when the power supply is started, the switching transistor Q
The inrush current flowing into the circuit at the time of startup is suppressed by utilizing the constant current characteristic due to the collector saturation current of No. 1. Therefore, FIG.
According to the circuit of (1), it is possible to configure a power supply device in which loss generated when driving the current control element is small and inrush current is small.

FIG. 2 shows a circuit of a switching power supply according to a second embodiment of the present invention. The circuit shown in FIG.
Compared to the circuit shown in FIG. 1, the current detection circuit 6b has the following configuration. That is, the detection resistor R8 is connected between the output terminal 2 and the connection point between the choke coil L1 and the output capacitor C2 to which the primary winding N1 of the current transformer CT is connected in the circuit of FIG. A series circuit of resistors R9 and R10 is connected between one end of the detection resistor and the ground,
A series circuit of resistors R11 and R12 is connected between the other end of the resistor 8 and the ground. An error amplifier EA is provided, one input terminal of which is connected to a connection point between the resistors R9 and R10, and the other input terminal is connected to a connection point between the resistors R11 and R12. The output terminal of the error amplifier EA is connected to the base of the control transistor Q4 via the resistor R6.

2 and 1 have the same circuit configuration except for the current detection circuit 6b. The circuit shown in FIG. 2 amplifies a difference between voltages appearing at both ends of the detection resistor R8 by an error amplifier EA to obtain a current detection signal corresponding to an output current. Although the circuit of FIG. 2 differs from that of FIG. 1 in the detection form of the output current, the operation of the other circuit portions is the same as that of the circuit of FIG. 1, and a detailed description of the operation is omitted.

FIG. 3 shows a circuit of a switching power supply according to a third embodiment of the present invention. The circuit shown in FIG.
Compared with the circuit of FIG. 1, the resistor R4 is removed from the circuit,
A resistor R is connected in parallel with the main current path of the control transistor Q4.
13 are connected. This resistor R13 forms a current bypass circuit 8, and the circuit of FIG. 3 is provided with a current bypass circuit 8 instead of the bias circuit 7. 3 and FIG. 1 have the same circuit configuration except for the bias circuit 7 and the current bypass circuit 8.

In such a configuration, when a voltage is supplied to the input terminal 1 from the outside, the control circuit 3 starts operating and causes a predetermined on-duty drive signal to appear at its pulse output terminal PO. In the circuit of FIG. 3, when the voltage at the position of the pulse output terminal PO is low, the driving transistor Q3 is turned on, and the first path from the base of the switching transistor Q1 to the ground via the driving transistor Q3 and the resistor R13 and , Switching transistor Q
A base current of the switching transistor Q1 flows from a base of the switching transistor Q1 to a ground via the driving transistor Q3 and the control transistor Q4. Therefore, the switching transistor Q1 is connected to the pulse output terminal PO
The bias is applied by the base current flowing through each path in accordance with the drive signal that appears in the above, and the on / off operation is performed.

When the voltage between the terminals of the capacitor C4 is almost zero immediately after the start, the control transistor Q4 is off, and the base current of the switching transistor Q1 is determined by the series resistance value of the resistors R3 and R13. Here, if an element having a high resistance value is used for the resistor R13,
The base current of the switching transistor Q1 has a small value according to the resistance value of the resistor R13, and the peak value of the current passing between the emitter and the collector is limited to a small value. When the switching transistor Q1 is turned on by the base current passing through the resistor R13, power transmission from the input terminal 1 side to the output terminal 2 side is started. Then, a current flows through the primary winding N1 of the current transformer CT, a voltage is induced on the secondary winding N2, and the capacitor C4 is charged via the diode D2. The voltage appearing between the terminals of the capacitor C4 is applied as a detection signal corresponding to the output current to the base of the control transistor Q4 via the resistor R6.

When the voltage between the terminals of the capacitor C4 rises, the control transistor Q4 conducts, and a current also flows through the main current path of the control transistor Q4. As the voltage between the terminals of the capacitor C4 increases, the current passing through the control transistor Q4 increases, and the total base current of the switching transistor Q1 gradually increases. Then, the peak value of the current passing through the main current path of the switching transistor Q1 gradually increases, and more current is supplied to the external load connected to the output capacitor C2 and the output terminal 2. After the output voltage and the output current are stabilized after a predetermined period, the circuit shown in FIG. 3 enters a steady operation state.

In a steady operation state, for example, when the load connected to the output terminal 2 reaches the maximum operation state, the output current of the circuit shown in FIG. 3 becomes very large. Then, the terminal voltage of the capacitor C4 charged by the current supplied from the secondary winding N2 of the current transformer CT increases, and the control transistor Q4 is turned on. When the control transistor Q4 is turned on, the switching transistor Q1
Has a maximum value substantially determined only by the resistor R3. On the other hand, when the load connected to the output terminal 2 has a minimum load state close to no load, the output current of the circuit shown in FIG. 3 becomes very small. Then, the capacitor C4
Becomes low, and the control transistor Q4 is turned off. When the control transistor Q4 is turned off, the base current of the switching transistor Q1 becomes the resistance R3
And the minimum value determined by the series resistance value of the resistor R13.

As a result, when the load is heavy, the base current of the switching transistor Q1 increases, and the output current required by the load is secured. On the other hand, when the load is light, the base current of the switching transistor Q1 is narrowed down, and the power loss generated in the circuit portion through which the base current flows is reduced. That is, the circuit of FIG. 3 changes the base current of the switching transistor Q1 in accordance with the output current required by the load, and thus the flow rate of the current that must pass through the main current path of the switching transistor Q1, similarly to the circuit of FIG. It operates to flow only the required amount. Additionally, at the time of starting the power supply device, the inrush current flowing into the circuit at the time of starting is suppressed by utilizing the constant current characteristic due to the collector saturation current of the switching transistor Q1.

In the circuits shown in FIGS. 1 to 3 described above, the driving circuit 4 is connected to the first driving transistor Q2 and the second driving transistor Q2.
Is constituted by a circuit in which the driving transistor Q3 is complementarily connected. However, it is not always necessary to adopt this circuit configuration in practicing the present invention. For example, one of the two driving transistors may be omitted, and a position where the main current path of the omitted driving transistor is connected may be used. A circuit configuration for connecting a resistance element having a relatively high electric resistance may be used. Further, as a power supply device to which the present invention is applied,
In the circuits of the respective embodiments, a step-down chopper type converter circuit is illustrated. However, the power supply device to which the present invention can be applied is not limited to this, and is also applicable to an insulated switching power supply circuit using a boost chopper type converter circuit or a transformer.

In the circuit of the embodiment shown in each figure, a resistor R7 is connected between the base of the control transistor Q4 and the ground.
Is connected, for example, a constant voltage diode element may be connected instead of the resistance element, or may be omitted in some cases. In the circuit of the embodiment shown in FIGS. 1 and 2, the resistor R3 limits the base current of the switching transistor Q1, and the capacitor C3 is a speed-up capacitor. Therefore, the parallel circuit of the resistor R3 and the capacitor C3 is composed of the base of the switching transistor Q1 and the control transistor Q3.
It only needs to be connected on the current path connecting the emitters of
The operation of the circuit does not change depending on the connection position.

In the circuit of the embodiment shown in each figure,
The other end of the first bias circuit 4 is connected to the pulse output terminal PO of the control circuit 3 to supply a drive signal directly to the base of the switching transistor Q1. However, a circuit in which a drive circuit including a transistor whose base is connected to the pulse output terminal PO is connected in series to the first bias circuit 4, and a drive signal is indirectly supplied to the base of the switching transistor Q1. It may be configured. As described above, the power supply device according to the present invention is not limited to the circuit configurations shown in FIGS. 1 and 2 and can be variously modified without changing the paper of the present invention.

[0030]

As described above, the switching power supply according to the present invention includes a drive circuit, a current detection circuit, and a limiter circuit, and further includes one of a bias circuit and a current bypass circuit. And the amount of bias supplied to the current control element via the current detection circuit is changed according to the output current detected by the current detection circuit. According to such a configuration, a bias having a magnitude required at that time is supplied to the current control element without waste according to the flow rate of the current that has to pass through the main current path of the current control element. As a result, power loss generated when driving the current control element can be reduced.
Also, it is possible to suppress an inrush current generated at the time of starting the apparatus. Therefore, according to the present invention, a highly efficient and highly safe power supply device can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power supply device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a power supply device according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a power supply device according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram of an example of a conventional power supply device.

[Explanation of symbols]

1: input terminal 2: output terminal 3: control circuit
4: Drive circuit 5: Limiter circuit 6a, 6b: Current detection circuit
7: Bias circuit 8: Current bypass circuit C2: Output capacitor
C4: Capacitor (capacitance element) CT: Current transformer EA: Error amplifier PO: Pulse output terminal Q1: Switching transistor (current control element) Q2, Q3: Driving transistor Q4: Control transistor R6: Resistance (resistance element) R8: Detection resistance

Claims (4)

[Claims] 1. A power supply device for changing a flow rate of a current passing through a current control element in accordance with a signal from a control circuit to obtain a desired output voltage, comprising: a pulse signal having an on-duty having a magnitude corresponding to the output voltage; A driving transistor having a control terminal connected to the control circuit, and one end of a main current path connected to a control terminal of the current control element, in response to a pulse signal from the control circuit. A driving circuit for supplying a bias to the current control element, a current detection circuit for outputting a detection signal corresponding to the magnitude of the output current of the power supply device, a current detection circuit connected to the driving circuit, and the current flowing through the driving circuit. A limiter circuit for changing an amount of bias supplied to the control element in accordance with a detection signal from the current detection circuit. 2. A control transistor having a main current path connected between the drive circuit and a reference potential point, and a limiter circuit connected between a control terminal of the control transistor and the current detection circuit. The power supply device according to claim 1, further comprising a resistance element. 3. The power supply device according to claim 1, wherein a bias circuit is connected between a control terminal of the current control element and the control circuit. 4. The power supply device according to claim 2, wherein a current bypass circuit is connected in parallel to a main current path of the control transistor.